No one really knows the extent of the effects of illness uncertainty on the emotional well-being of chronically disabled people. Nursing needs to fill this void, a need this study aims to meet. The purpose of this research is to explicate the processes through which chronic disability acts to affect emotional well-being so as to develop the theoretical foundation upon which to base effective nursing interventions. The specific aims involve answering these questions: 1) What is the relationship between illness uncertainty and emotional well-being in chronically disabled individuals, while controlling for the effects of functional disability, personal resources, social resources, daily hassles, stress appraisal, coping, and selected demographic and antecedent variables? 2) What are the similarities and differences in these relationships between individuals with a chronic disability having a predictable trajectory (spinal cord injury or SCI) and those with an unpredictable one (multiple sclerosis or MS)? The chosen populations are well suited for the investigation of illness uncertainty because of the extremes they represent with respect to predictability. A combination of study designs, the comparative survey and the panel design, will be used. Subjects consenting to participate will be involved in three, two-hour semi-structured home interviews over a three-year period conducted by a trained interviewer. The four year study (1/90 through 12/93) collects data at one-year intervals. The final population size desired at the third data collection is 672 (343 with MS and 332 with SCI). The design makes it possible to study the dynamic relationships affecting well-being as these relationships unfold, while also making it possible to compare and contrast the two cohorts. The pattern of relationships among the variables will be examined cross-sectionally and longitudinally, primarily using multiple regression and structural equation modeling (LISREL). The theory generated by this research may be useful in guiding nursing practice through the specification of the processes affecting emotional well-being. In the long run, these findings may also help maximize preventive interventions though the identification of individuals at risk for the deleterious effects of disability.